This torque adapter allows you to use your nozzle wrench to measure the torque.  It measure the tightening torque and can undo the nozzle too. It doesn't mind a bit of heat. Really easy to assemble and use. Does need a calibration step but only once for each spring.

It needs 

• A spring with OD less than 10mm (mine came from a hand soap pump bottle)
• A nozzle wrench (online, I bought a 6 and 7 mm version for less than $3)
• Printed part

Files

There are 2 versions, 

• One is for a stiffer spring, mine gave about 2.5mm of compression for 1 Nm of torque
• The other is wider for a softer spring, my spring gave about 8mm for every 1 Nm of torque and is obviously more accurate to use with the wider spacing.

You can test your spring by seeing how much it compresses when a known weight is applied. This adapter with its 88mm long wrench has a conversion factor of 0.86 Nm per kg (calculated from 0.98 x 0.088). So when 1 kg of weight is applied to the spring, the torque will be 0.86Nm.

Both adapters will work with a range of springs but if your spring is short you will likely want the narrower version.

STP files are included if you need to do some adjustment.

The slide is to apply even pressure to the spring from the wrench

 Print the part 

I suggest you use supports, especially for the wider version. For the narrow version I didn't use supports and the back spring compartment bridged without trouble. If you print too hot you may have to do some cleanup inside. My print took 1 hour at 0.28mm layer thickness.

I added the scale embossing, printing with 0.25mm layer height showed it up clearly as you can see in one of the pictures.

Calibration

Method 1

I used a kitchen scale, a paint stirrer stick, some heavy objects and a reel of filament.

The flat paint stirrer is the platform that the weights stand on.

• Place the spring in the centre of the scale and position the paint stirrer on it. Tape the other end to stop it moving but it can still pivot.
• Tare the scale
• Measure the height of the stick.
• Add a weight and record the new height. Remove the ruler when you read the weight.
• Add more weights and record the heights (which decreases as the weight increases)

The weight doesn't have to be exactly over the spring, the scale will read less if the weight is nearer the spool of filament. That's OK, the scale measures the weight applied to the spring and that's what you want to record to match the amount of spring compression.

When you've made a few measurements up to about 2.5kg you can make a graph that will tell you how much torque will give what displacement of the spring. The lever arm is 88mm long from the centre of the hex socket to the centre of the spring.

Method 2

This is simply an easier way of doing method 1.

• Set your vernier to a few mm less than the length of the spring.
• Use the depth tool (long thin end that sticks out the back of the vernier) depress the spring, on the scale till the end touches the scale face.
• Record the scale reading at which the vernier depth tool touched the scale.  Be careful to read the weight just before the long thing probe touches the scale or you will be adding weight that the spring doesn't feel. If you know how to use your vernier to set a zero at the spring length you can read the displacements directly
• Do this for a few readings, ideally you want to measure the depth at T x 1.1 kg where T is the torque you want to use.

If you draw your graph of displacement from the uncompressed length of the spring now you should have a fairly straight line. for weight vs displacement. 

Method 3

I have a set of ball nose Allen keys, the 6mm wrench is 137mm from the centre of the short arm to the start of the ball. Insert the Allen wrench into the nozzle wrench (in the adapter). I then hang a plastic shopping bag in the narrowing for the ball part and put 1, 2, 3, or 4 355ml pop cans in the bag. This applies 0.5, 1, 1.5 and 2 Nm of torque.

I used some tape to mark the torque readings. You can just mark the top with a fine marking pen, you really only need one mark anyway.

Improvements and remixes

• Maybe a screw to adjust the spring. 
• Rounder corners to ease the grip. 
• Electrical contacts to light a LED when the desired value is reached. 
• A dial indicator or depth gauge for the measurement, get really accurate torque measurements

Get creative and have fun.